Human Milk Composition
Infant and Young Child Feeding
B.Sc. (Hons.) Human Nutrition and Dietetics
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Contents
• Human Milk Composition
• Stages of Lactation
• Breast Milk Vs. Formula Milk
• Nutritional Components of Human Milk
• Macronutrients
• Micronutrients
• Bioactive Components
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Human Milk Composition
• Contains thousands of distinct bioactive molecules that
Reduce Morbidity and mortality
Protect against infection and inflammation
Contribute to immune maturation, organ development, and healthy
microbial colonization
• Some of these molecules, e.g., lactoferrin, are being investigated as
novel therapeutic agents.
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Stages of Lactation
Colostrum Transitional Mature
Milk Milk
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Colostrum
• The first fluid produced by mothers after delivery is colostrum
• Rich in immunologic components such as
Secretory IgA
Lactoferrin
Leukocytes
Developmental factors such as epidermal growth factor
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• Colostrum also contains relatively low concentrations of lactose,
indicating its primary functions to be immunologic rather than
nutritional
• Levels of sodium, chloride and magnesium are higher and levels of
potassium and calcium are lower in colostrum than later milk.
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• As tight junction closure occurs in the mammary epithelium, the
sodium to potassium ratio declines and lactose concentration
increases, indicating secretory activation and the production of
transitional milk.
• The timing of secretory activation (lactogenesis stage II) varies among
women, but typically occurs over the first few days postpartum
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Transitional Milk
• Transitional milk shares some of the characteristics of colostrum but
represents a period of “ramped up” milk production to support the
nutritional and developmental needs of the rapidly growing infant, and
typically occurs from 5 days to two weeks postpartum
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Mature Milk
• By four to six weeks postpartum, human milk is considered fully
mature
• In contrast to the dramatic shift in composition observed in the first
month of life, human milk remains relatively similar in composition,
although subtle changes in milk composition do occur over the course
of lactation
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Mother Milk Vs. Formula Milk
• Unlike infant formula, which is
standardized within a very narrow range
of composition, human milk
composition is dynamic, and varies
within a feeding, diurnally, over
lactation, and between mothers and
populations.
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Compositional Differences
• Influences on compositional differences of human milk include
Maternal factors
Environmental factors
Milk expression
Management of milk
(e.g., Its storage and pasteurization)
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Nutritional Components of Human Milk
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Sources of Diversity
• The nutritional components of human milk derive from three sources:
• Some of the nutrients of milk originate by synthesis in the lactocyte,
• Some are dietary in origin
• Some originate from maternal sources
• Overall, the nutritional quality of human milk is highly conserved, but
attention to maternal diet is important for some vitamins and the fatty
acid composition of human milk 14
Macronutrients
• The macronutrient composition of human milk varies within mothers
and across lactation but is remarkably conserved across populations
despite variations in maternal nutritional status
• Energy estimates range from 65 to 70 kcal/dL, and are highly
correlated with the fat content of human milk
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Preterm (Premature) milk
• Milk from women who deliver prematurely differs from that of
women who deliver at term.
• Preterm milk is initially higher in protein, fat, free amino acids, and
sodium, but over the first few weeks following delivery these levels
decrease.
• The premature milk is higher in protein and minerals, such as salt, and
contains different types of fat.
• The fat in human milk helps to enhance the development of the baby's
brain and neurologic tissues, which is especially important for
premature infants.
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Term milk
• Term milk approximately contains
• 0.9 to 1.2 g/dL for protein
• 3.2 to 3.6 g/dL for fat
• 6.7 to 7.8 g/dL for lactose
• Macronutrient composition differs between preterm and term milk,
with preterm milk tending to be higher in protein and fat
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• A study in Davis, California examined the association between
maternal characteristics and the composition of human milk
macronutrients and found that after 4 months postpartum, the
macronutrient concentrations of human milk are associated with one
or more of the following factors:
• Maternal body weight for height • Return of Menstruation
• Protein intake • Nursing frequency
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• This study also found that mothers who produce higher quantities of
milk tend to have lower milk concentrations of fat and protein but
higher concentrations of lactose.
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Proteins
• The proteins of human milk are divided into the
• Whey
• Casein fractions
• Casein complexes, with each comprised by a remarkable array of
specific proteins and peptides
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• The most abundant proteins are
• Casein
• Α-lactalbumin
• Lactoferrin
• Secretory immunoglobulin iga,
• Lysozyme
• Serum albumin
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• Non-protein nitrogen-containing compounds comprise ~25% of human
milk nitrogen including
• Urea
• Uric acid
• Creatine
• Creatinine
• Amino acids
• Nucleotides 23
Protein
• Human milk protein concentration is not affected by maternal diet, but
• Increases with maternal body weight for height
• Decreases in mothers producing higher amounts of milk
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Fat
• Human milk fat is characterized by high contents of palmitic and oleic acids
• Fat is the most highly variable macronutrient of milk
• Hind milk, defined as the last milk of a feed, may contain two to three times the
concentration of milk fat found in foremilk, defined as the initial milk of a feed
• The fatty acid profile of human milk varies in relation to maternal diet,
particularly, in the long chain polyunsaturated fatty acids
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Carbohydrates
• The principal sugar of human milk is the disaccharide lactose
• The concentration of lactose in human milk is the least variable of the macronutrients
• But higher concentrations of lactose are found in the milk of mothers producing
higher quantities of milk
• The other significant carbohydrates of human milk are the oligosaccharides, which
comprise approximately 1 g/dL in human milk, depending on stage of lactation and
maternal genetic factor
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Micronutrients
• Many micronutrients vary in human milk depending on maternal diet and body
stores including vitamins A, B1, B2, B6, B12, D and iodine
• The maternal diet is not always optimal, thus, continuing multi-vitamins
during lactation is recommended
• Regardless of maternal diet, Vitamin K is extremely low in human milk
• The American Academy of Pediatrics recommends an injection of this vitamin
to avoid hemorrhagic disease of the newborn
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• Vitamin D also occurs in low quantity in human milk, particularly
with low maternal exposure to sunshine
• While the impact of maternal supplementation with vitamin D on milk
composition is under investigation
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Bioactive Components
Bioactive components of food are defined as elements that “affect
biological processes or substrates and hence have an impact on body
function or condition and ultimately health
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• Bioactive components in human milk come from a variety of sources
1. Produced and secreted by the mammary epithelium
2. Produced by cells carried within the milk
3. Drawn from maternal serum and carried across the mammary
epithelium by receptor-mediated transport
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• Major Bioactive Factors in Human Milk
• Cells
• Immunoglobulins
• Cytokines
• Growth Factors
• Hormones
• Metabolic hormones
• Oligosaccharides & glycans
• Mucins 31
Summary
• Human Milk Composition
• Stages of Lactation
• Breast Milk Vs. Formula Milk
• Nutritional Components of Human Milk
• Macronutrients
• Micronutrients
• Bioactive Components
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